Internal water tank solar heat exchanger

ABSTRACT

A heat exchanger which is adapted to an existing water tank to allow it to be heated or cooled using a hot or cold toxic or non-toxic liquid. Solar collectors, other heat sources and heat pumps can provide hot or cold liquids. To transfer this heat economically to an existing hot water tank requires a simple, efficient, heat exchanger, which can be easily adapted to the existing tank. The invention recited fills this need by simply screwing into the existing hot or cold water tank and allows heat or cold to be added or extracted via a simple fluid loop which is double wall isolated for toxic and non-toxic heat exchange fluids.

BACKGROUND OF INVENTION

Continuation in part application Ser. No. 10/085,174 includes the allowed specifications, claims and figures already a part of the prior application by reference. This patent continuation in part includes three added features, first a union connection to the hot water tank outlet, to allow heat exchanger placement into the tank without rotation, second foldable/bendable fins, pins or foils on the outer surface of the heat exchanger to allow for greater heat transfer area in the between the heat exchangers external surface and the water in the hot water tank, and third the addition of an integral zinc or other suitable material as a built-in sacrificial anode. Natural convection internal, double walled, heat exchangers for existing hot water tanks are needed to adapt in-home hot water tanks to modern solar collector heat sources. This invention pertains to the input or extraction of heat from an existing storage tank, which is plumbed into an existing “city” pressure water system for home or industrial use. Heat is transferred from a heated or cooled fluid in a separate heat transfer loop, which is not pressurized by “city” water pressure and must be separated from it by two walls to prevent contamination. If the heated or cooled fluid is toxic, then double wall isolation from potable water is needed. This invention allows an existing hot water tank to be adapted for heating by a solar energy heated fluid or a heat pump heated fluid, without modifying the existing tank except by placing an adapter between it and an output water line at “city” pressure. This use of an existing tank can help to reduce the cost of solar hot water heating and heat pump hot water heating. The adapter could also be placed on the cold-water inlet, water drain port or other water tank standard port.

PRIOR ART

For current solar systems the most common liquid to existing hot water tank heat exchangers are either external pumped or natural convection. The external pumped heat exchangers pump water from the tank past the heat exchanger and return it to the tank. This is efficient but requires plumbing and a pump and control electronics. External pumped heat exchangers disturb the tank's normal stratification, hotter on top, cooler on bottom. External convection heat exchangers eliminate the pump but not the plumbing. In addition, the plumbing required to keep the convection loop working requires the buoyancy difference between hot and cold water to drive it. The flow resistance in piping is small, but so are the buoyancy forces. Hence, heat transfer is less efficient. Special tanks with built-in double walled heat exchangers are available but this requires that the existing tank be replaced. Tanks in use have long, 20 year, life expectancies. The recited invention can be screwed onto or fitted into any existing tank and provide it with liquid-to-liquid heat exchange capability.

The invention allows any hot or cold water tank fitted with standard pipe threaded ¾ inch NPT or larger outlets/inlets to be used as a source, or sink, for heat from toxic heat exchange fluids while meeting USA building and plumbing codes for double wall separation of toxic fluids and potable water. Heat exchangers of the internal tank type are preferred for solar collectors and liquid to air heat pumps. The invention recites that all heat exchanger plumbing is within the hot water tank. All heat leaving or entering the exchanger goes to or comes from the hot water tank. Externally plumbed heat exchangers must be well insulated to avoid heat loss to the surrounding air. They need two connections to the tank and a plumbing system. Natural convection systems are much less efficient. Pumped external heat exchangers are more efficient than natural convection. However, the pump costs a lot more and disturbs the tank's natural stratification. Natural convection internal and external heat exchangers preserve the tank's natural stratification. It is important not to disturb the normal tank stratification because it decreases the normal gas or electric heater efficiency. Main advantages of this invention are: 1) adapts to existing tanks with minimum re-plumbing and without tank removal or draining; 2) is efficient; 3) safely separates toxic heat transfer fluids from potable water; 4) costs less to install and maintain; and 5) maintains normal tank stratification.

SUMMARY OF INVENTION

In summary, the present invention is a heat exchange adapter that can be screwed into the standard pipe fitting on existing city line pressurized water tanks. These standard pipefittings include the city water inlet, hot water outlet, sacrificial anode port, pressure relief port, and tank drain port. This heated/cooled liquid is pumped through the in-tank heat exchanger, which is surrounded by tank water and transfers heat to the tank via conduction through the heat exchanger walls and then natural convection into the tank water. This invention also includes foldable or flexible/bendable elements attached to the water tank side of the heat exchanger to increase the surface area of heat exchanger in contact with the tank water. The foldable or flexible/bendable elements can extend out to be larger in diameter than the opening into the hot water tank. They will be folded or bent to fit through the opening and then spring back to their original shape/size once inside the hot water tank, allowing greater heat transfer area inside of the hot water tank. This invention may also include a union on the heat exchanger that will allow the heat exchanger to be screwed into the tank without rotating the heat exchanger element. This allows the heat exchanger to be deformed or bent to avoid obstacles inside the tank and not be rotated once inserted into the hot water tank. The wand can be inserted through a side port and be bent from horizontal to vertical to go up or down into the tank. This invention may also include an attached sacrificial anode which makes electrical contact with the heat exchanger in a configuration that will allow it to be inserted into the hot water tank. The heated/cooled liquid is connected to the adapter fluid lines and pumped into the in-tank heat exchanger and then back out of the tank. The heat exchanger adapter may reduce the plumbing water flow in gallons/minute by up to 50%. Water conservation measures, low flow showerheads and appliances, have already reduced hot water flow requirements so the flow reduction will have minimum impact on the homeowner.

The primary objective of the present invention is to allow existing water tanks to be adapted to take solar heating and other forms of heating without moving or replacing the existing tank. Another objective is to reduce the time and complexity of retrofitting solar energy, or other forms of heating to existing homes with a hot water tank in place.

Additional objectives, advantages and novel features of the invention will be set forth in part in the description which follows and in part will become apparent to those skilled in the art upon examination of the following. In particular, the heat exchanger tubing geometries may be spiraled or formed differently, but are still included in this patent. Others may be learned by practice of the invention. The objectives and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.

DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the heat exchange adapter showing the tank fitting and new tank input or output and the heating/cooling fluid connections.

FIG. 2 is a cutaway view of the double wall heat exchanger cross section.

FIG. 3 shows alternative inner and outer wall configurations

FIG. 4 (New) shows a coupling union and sacrificial anode added to the cutaway view of the double wall heat exchanger cross section shown in FIG. 2.

FIG. 5 (New) show alternative inner and outer wall configurations which increase the heat transfer surface area in contact with the water in the hot water tank.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The invention consists of a screw in T-adapter (6), which replaces the hot water tank outlet (24) or coldwater inlet (28) lines. (FIG. 1) The water exits (or enters) the tank (22) now via a side arm of the adapter (26). Toxic or non toxic heating or cooling fluid (13), flows in small tubes (14 & 17), which go into the tank (14) and return (17) encased in an outer second tube labeled (16). Inside the tank, the tube labeled (16) has been deformed to make physical contact with the toxic fluid carrying tubes labeled (14 & 17). Heat is conducted between the toxic heat exchange fluid to or from the potable water. Because of the double wall design, toxic fluid leaking from tube (14 & 17) will not reach the potable water; it is stopped by tube wall (16). If a leak of potable water occurs, it is at high pressure and would again be leaked outside the tank between tubes (14 & 17) and second wall (16). This assures no chance for contamination of potable water with toxic heat transfer fluids, even if the heat transfer fluid is under high pressure. A leaking heat exchanger would be replaced. Note that tube (16) containing tubes (14 & 17) is configured to fit through the female pipe threaded tank fitting, labeled (24).

The cross section of the double wall heat exchanger (FIG. 1) A-A shows potable water (30), on the outside, tube (16), deformed around heat transfer tubes (14 & 17). The interface (32) between tubes (14 & 17) and (16) is a mechanical one which transfers heat by areas of metal to metal contact with thin metal oxides or other heat conducting material at the metal to metal interface forming fluid flow channels.

FIG. 2 shows a cutaway view of the double walled heat exchanger cross section. This design includes a tube (14) to deliver the fluid (13) to the bottom of tube (17) with an annular space to return the fluid (13) to the top. Spiral fluting on tube (16) allows tube (16) to contact tube (17) for good heat transfer and large surface area to potable water (30). Leaking liquid from tubes (16) or (17) is free to move along interface (32), and will move along interface (32) and overflow out of the top of coupling (6) outside of the water tank (22) between tubes (16) and (17).

FIG. 3 shows tube (14) inside tube (17) configuration 46 and alternative ways to deliver the heat in the heat transfer fluid (13) to the inner walls (14 & 17 in configuration 44) or (17 in configuration 42), which will be in physical contact with the inside of outer wall (16). They are labeled (44) Double D and (42) Tube With Separator. The separator (15) ends before the bottom of tube (17) so the fluid (13) can turn around at the bottom and head back up. The outer wall configurations are limited in diameter including appendages to fit through opening (24) into the existing hot water tanks (22). Spiral-fluted rolled fins are shown in FIG. 3 (52), alternatives are shown as FIG. 3. Vertical (54) and horizontal (56) variations of rolled fins on the outer wall (16) are shown.

FIG. 4 shows the same cut away view as FIG. 2 but with the addition of a standard (female threaded) pipe union (23) consisting of the top flange (31), bottom flange (27) and flange coupling nut (25). A pipe nipple (29) is shown between the standard pipe union (22), bottom flange (27) and the top of the water tank outlet fitting (24). The heat exchanger assembly is inserted into the hot water tank through fitting (24). The bottom flange (27) of standard union (23) and threaded pipe nipple (29) are screwed tight into hot water tank top fitting (24), with the flange coupling nut (25) loosened so the upper flange (31) does not rotate with the lower flange (27). The lower flange (27) is coupled securely (leak tight) into the hot water tank top fitting (24) via nipple (29). Then the upper flange (31) is firmly coupled to the T-adapter (6), Once the lower flange (27) and upper flange (31) are firmly in place, then the flange coupling nut (25) can be tightened, locking the upper flange (31) and lower flange (27) making a water tight seal, without any relative rotation of the upper flange (31) and the lower flange (27) with respect to each other. This allows the heat exchanger to be put in place, without rotating the T-adapter (6). This same process for insertion can be used to put the heat exchanger assembly into a hot water tank fitting which is on the side of the hot water tank.

FIG. 4 also shows the addition of a sacrificial anode (33) to the bottom end of the outer wall (16) of the heat exchanger. It is usually made of zinc or high zinc alloy and is metallurgically attached (welded, brazed or soldered), so the sacrificial anode makes good electrical contact with outer wall (16) and is held firmly in place. As an alternative to the design shown in FIG. 4, the sacrificial anode can be placed in the flutes or flexible elements for insertion and spring out after insertion, as long as it is electrically connected to outer wall (16), FIG. 5 shows additional configurations of the outer wall of the heat exchanger, which allow for increased heat transfer area between the outer wall (16) and the water in the hot water tank (30), The foldable or collapsible elements attached to the outer wall (16) by bonding, soldering or welding or other means, The elements can be pins, foil sheets, cut foil sheets, which add heat transfer surface to the outer wall and promote heat transfer to the hot water tank. These elements must be capable of bending like the bristles of a broom, to fit through the port into the hot water tank, and then must spring back out to present more heat transfer surface to the water in the hot water tank. The heat transfer area increasers are labeled flexible/foldable foil sheets (48), flexible/bendable bristles (50) and flexible/bendable foil fins (51), which are attached to the outer wall (16) and radiate into the hot water tank to transfer heat to the water they come in contact with. In flexible/foldable foil sheets (48), the appendages are foil sheets (35) which are continuous or discontinuous over the axial length of the outer wall (16). These sheets (34) are folded tightly to the outer wall (16) as shown by the small arrows (32) for insertion into the hot water tank. Once inside the hot water tank, the foils spring back to the positions shown in (48). In flexible/bendable bristles (50), the appendages are bristles (36) like those on a bottle brush. Each bristle (36) bends as it goes through the hot water tank opening (FIG. 4 (24)) and then springs back to carry heat from outer wall (16) out along the bristle's length (36), and conducted into the water (30) as water (30) flows by natural convection over the bristles (36). In flexible/bendable foil fins (51), the appendages are bent foil tabs (40) which are attached to outer wall (16). These foil tabs can be formed easily by cutting a single ribbon (39) and spiral wrapping (40) the foil fins along the length of outer wall (16). These flexible/bendable foils bend as they go through the hot water tank opening (FIG. 4 (24)) and then spring back to carry heat from outer wall (16) out along the foil's length (38) and conducted into the water (30) as water(30) flows by natural convection over the foil (38).

The inner wall configurations are shown as tube with separator (42), double-D tubes (44) and the spur tube (tube in tube) (46). Configuration (46) spur tube was elected for the original patent. Configurations (44) and (42) are alternatives, which provide similar paths to conduct fluid (13) along the inner wall (17) of the heat exchanger. 

1. An insertable double wall, in-tank heat exchange adapter for existing water tanks, comprised of a heat exchanger having a tubular element, an inlet, and an outlet defining a flow path for heat exchange fluid; an adapter on which said heat exchanger is mounted; said adapter having a male threaded portion surrounding an open port through which said heat exchanger extends adapted to screw into a threaded port provided on a water tank; and an outlet/inlet port provided on the adapter surrounded by a complementary female (or male) threaded portion which matches the male threaded portion and communicates with the open port to allow the supply or withdrawal of fluid to or from the tank when the adapter is connected thereto.
 2. An insertable heat exchanger according to claim 1 which has double isolated heat exchange fluid tubes and a path for all leaking water or heat exchange fluids to exit outside of the water tank.
 3. An insertable in-tank heat exchanger according to claim 1 in which the second heat exchanger wall is formed with flexible/foldable foil sheets, or flexible/bendable bristles, or flexible/bendable foil fins, which can be collapsed or bent for insertion and fold out or spring back in the hot water tank to increase the heat transfer surface in contact with the water to be heated.
 4. A union type coupling to allow the heat exchanger according to claim 1 to be inserted with an adapter union so it does not need to be rotated inside the tank and can be bent to allow insertion from both top and side ports and to avoid other tank inserts, such as heating elements and temperature measuring devices.
 5. An insertable in-tank heat exchanger according to claim 1 in which the second heat exchanger wall is formed of flexible/foldable foil sheets.
 6. An insertable in-tank heat exchanger according to claim 1 in which the second heat exchanger wall is formed of flexible/bendable bristles.
 7. An insertable in-tank heat exchanger according to claim 1 in which the second heat exchanger wall is formed of flexible/bendable foil fins.
 8. An insertable in-tank heat exchanger according to claim 1 which screws into the sacrificial anode port and has an integral sacrificial anode built into it.
 9. An insertable in-tank heat exchanger according to claim 1 with fluid tubes shaped as D's back to back, to form a round core.
 10. An insertable in-tank heat exchanger according to claim 1 with fluid tubes formed from a single tube with an internal separator.
 11. An insertable in-tank heat exchanger according to claim 1 with fluid tubes formed as a spur tube (tube inside a tube), with fluid flowing inside the center tube and returning in the annular space or vice versa.
 12. An insertable in-tank heat exchanger according to claim 1 in which the second heat exchanger wall is formed as spiral flutes.
 13. An insertable in-tank heat exchanger according to claim 1 in which the second heat exchanger wall is formed as stacked flutes.
 14. An insertable in-tank heat exchanger according to claim 1 in which the second heat exchanger wall is formed as columnar flutes. 